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The Aruch Hashulchan paskens like common practice that it is permitted (see here and here), justifying it as follows:

The Arukh Ha-Shulchan (Orach Chaim 151:5) asked why people speak idle chatter in (even non-Chassidic) synagogues after prayer services and answered that we must follow the view of the Ramban and Ran that when synagogues are founded with the condition that certain non-holy things will take place in them (such as eating or speaking idle chatter), then in cases of need these activities are permitted. And, continues the Arukh Ha-Shulchan, we must find these friendly discussions to be needed. He rules this way even though the Shulchan Arukh rules against the Ramban and Ran.

Edit: I would add that it seems that the Bach permits sichas chullin bein gavra legavra (see here for more), which surely takes place in a shul. My strong suspicion is that "sichas chullin" and/or "sicha beteila" is a homonym, and means different things to different people.

The parenthetical remark "(even non-Chassidic)" requires context from the preceding paragraph in Hirhurim: "The Tzanzer Rav... explains that Chassidim intentionally do not create synagogues but instead make communal buildings... in which to perform all of their communal functions, including prayer. Therefore, the stringencies of a synagogue do not apply to shtieblakh."
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FredJan 23 '13 at 23:06